U.S. Pat. No. 4,119,710 describes inter alia the racemate 1-(4'-amino-3'-cyano-phenyl)-2-isopropylamino-ethanol (generic name: cimaterol) and its pharmaceutical properties. Thus, the compounds described in U.S. Pat. No. 4,119,710 have, in addition to their analgesic and uterus-spasmolytic effects and their antispastic effects on the transverse-stripped musculature, in particular .beta..sub.2 -mimetic and/or .beta..sub.1 -blocking effects, with one or other effect being dominant depending on the substitution. It is also established in U.S. Pat. No. 4,119,710 that the d-(+)-compounds have in particular a selective effect on the .beta..sub.1 -receptors and the 1-(-)-compounds have a preferred effect on the .beta..sub.2 -receptors.
Moreover, U.S. Pat. No. 4,407,819, inter alia describes the performance-enhancing effect of cimaterol in animals.
It is also known that, normally, one of the two enantiomers of a racemate is more pharmacologically effective than the other enantiomer.
U.S. Pat. No. 4,119,710 describes two methods of separating the enantiomers of cimaterol, namely:
a) the resolution of a mixture of diastereomeric compounds which are obtained by reacting the corresponding racemate with a chiral acyl group, and subsequently cleaving the chiral acyl group, e.g. the (-)-methylcarbonyl group, or
b) the fractional crystallization of a mixture of diastereomeric salts, which are formed by reaction of the racemic base with an optically active auxiliary acid.
Racemate separation by method (a) is not thought to be promising since the cyano group present in cimaterol would be at least partially changed by hydrolysis or hydrogenolysis during the subsequent hydrolytic or hydrogenolytic cleaving of the chiral acyl group which would have to be carried out.
As is shown by the reference example which appears below, the conventional racemate separation, by method (b), does not resolve racemic cimaterol with good yields.